Full flow solenoid valve for air gun operation

ABSTRACT

The disclosure relates to a solenoid valve for an air gun which substantially increases the rate at which maximum air flow is achieved. The new valve structure includes a coil actuated plunger, which is preferably solid and formed of a magnetically permeable material and closes an annular 360 degree port opening between the valve inlet and valve outlet when in the unactuated state. This plunger position is maintained by a biasing spring which forces the forward annular sharp plunger edge against a face seal in the nose of the valve, thereby sealing the valve input port from its output port. Upon actuation of the solenoid valve coil, the plunger is moved against the bias of the spring very rapidly, thereby speedily uncovering the channel between inlet and outlet and permitting rapid 360 degree communication between the inlet and outlet to permit maximum air flow therebetween and out of the outlet port. Air flow is past the edge of the plunger and along an unimpeded 360 degree path rather than through a hollow stem. The importance of this is that the pressure provided by the solenoid valve builds up much faster and results in a much improved timing of the air gun firing (reduction in firing jitter).

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates to a solenoid valve and, more specifically, to asolenoid valve for use in conjunction with an air gun which is utilizedin seismic exploration.

2. BRIEF DESCRIPTION OF THE PRIOR ART

Air guns are well known in the field of seismic exploration, such airguns being used to provide a seismic wave which penetrates the earth'scrust and is reflected from the various strata therein. These reflectedwaves are analyzed to provide information as to the content and locationof the subterranean strata from which the reflection takes place.

In the operation of an air gun of the above noted type, as exemplifiedby the patent of Chelminski (U.S. Pat. No. 4,240,518), the solenoidvalve acts to trip a shuttle valve which, in turn, fires the gun. Therate of discharge of the high pressure solenoid valve air determines thespeed of shuttle release. Therefore, it is extremely important that thesolenoid valve discharge air flow rate be maximized. The importance of afast discharge rate is evidenced from the graph of FIG. 1 which is acomparison of the pressure supplied by a valve which provides full areaflow rapidly (full flow) as opposed to a prior art valve which graduallyincreases the flow rate until full flow is achieved. It can be seen thatthe time window (delta t1) during which the pressure is in the guntriggering pressure range is much shorter for a system wherein full flowis rapidly achieved as compared to the time window (delta t2) of theconventional valve wherein full flow is achieved slowly. This means thatthe more rapidly a valve can achieve full flow, the smaller will be thetriggering pressure range window, thereby increasing the accuracy ofdetermining the actual triggering time and improving the likelihood ofrepeatability. It is therefore apparent that the rise time of thesolenoid valve pressure is very important in reducing the firing timevariation (t) of the air gun. The slower the pressure rise time, thegreater the air gun firing time variation.

A reason for the relatively slow pressure rise time in conventional airgun solenoid valves is that the plunger slides on a center stem andgradually uncovers small drilled port holes in the stem as it travels.Uncovering of these holes provides a flow path for the discharging air,thereby gradually increasing the air flow rate from valve inlet to valveoutlet. Due to the location of the stem seal, the plunger must travel ashort distance before the ports begin to open, thus delaying the firingof the air gun. As the ports are continually opened, the flow areaincreases until it equals the flow area of the central hole of the stem.At that time, the flow area becomes the constant flow area of the stemholes.

It is readily apparent from the above discussion that improved accuracyin timing of the gun firing can be achieved by providing an air guncapable of rapidly achieving the maximum air flow rate capability of thesolenoid valve.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a solenoidvalve which substantially increases the rate at which maximum air flowis achieved, thereby providing the advantages flowing therefrom asenumerated above.

Briefly, in accordance with the present invention, the prior art hollowstem with port holes drilled therein and hollow plunger which uncoversthese port holes are replaced by a new structure wherein flow rateincreases linearly with plunger displacement. The new valve structureincludes a coil actuated plunger, which has no port holes therein, isformed of a magnetically permeable material and closes an annular 360degree port opening between the valve inlet and valve outlet when in theunactuated state. This stem position is maintained by a biasing springwhich forces the forward annular sharp edge thereof against a face sealin the nose of the valve, thereby sealing the valve input port from itsoutput port. Upon actuation of the solenoid valve coil, the plunger ismoved against the bias of the spring vary rapidly, thereby speedilyopening the channel between inlet and outlet and permitting rapid 360degree communication between the inlet and outlet to permit maximum airflow therebetween and out of the outlet port. Air flow is past the edgeof the plunger and along an unimpeded path rather than through a hollowstem. The importance of this is that the pressure provided by thesolenoid valve builds up much faster and results in a much improvedtiming of the air gun firing (reduction in firing jitter).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of pressure versus time for a solenoid valve showingthe triggering window for the full flow solenoid valve of the presentinvention compared with that of the conventional solenoid valve;

FIG. 2 is a plot of the flow area v. plunger displacement for theconventional solenoid valve and the valve of the subject invention; and

FIG. 3 is a cross-sectional view of a solenoid valve in accordance withthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 3, there is shown a cross sectional view of asolenoid valve in accordance with the present invention. The valveincludes a magnetically permeable housing 4, preferably formed ofstainless steel, which is secured over a pole piece 1 of magneticallypermeable material, preferably stainless steel. The pole piece 1includes a pair of grooves therein for receiving O-rings 19 whichprovides a seal with the housing 4.

Also disposed within the housing 4 is an annular solenoid coil 20, thecoil having leads 21 and 22 which extend externally of the valve forconnection to an external source for actuation of the valve. A furtherannular pole piece 18 which is formed of a magnetically permeablematerial, preferably stainless steel, is positioned adjacent the coil 20and retains the plunger 5 therewithin. The plunger 5 is axially movablewithin the pole piece 18 and is formed of magnetically permeablematerial, preferably stainless steel. The plunger 5 has a groove whichcarries an O-ring 3 for providing a seal therewith and with the polepiece 18. A magnetic circuit is formed from the first pole piece 1,across the air gap 17 and through the plunger 5 to the second pole piece18 and then to the housing 4 and back to the first pole piece 1. Acompression spring 2 is secured against the pole piece 1 and rests in ahollow region of the plunger 5 to bias the plunger against a face seal12. The face seal 12 is secured in the nose portion 7. A groove in thenose 7 carries an O-ring 11 which provides a seal between these elementsand pole piece 18.

A snap ring 6 is secured between the housing 4 and the nose 7 to keepthe plunger and nose from being pushed out by the spring. The snap ring6 hold the assembly together. A seal retainer 8 having a hollow centerportion is secured to the face seal and provides the outlet port 15 forthe valve. The seal retainer 8 prevents the face seal 12 from beingpushed into the outlet hole and retains the face seal. The inlet port 14to the valve extends to the valve chamber 16 via inlet passages 13, thevalve chamber being closed to the outlet 15 by the plunger 5 when thevalve has not been actuated. O-rings 9 and 10 provide a seal between thesolenoid valve and the portion of the air gun which applies air underhigh pressure to the valve inlet 14.

In operation, the air gun is pressurized to provide air at predeterminedpressure at the valve inlet 14, the air filling the valve chamber 16 atthe predetermined high pressure, typically 2000 psi. The air isprevented from discharging from the valve by the plunger 5 which is inthe spring biased position as shown in FIG. 3, closing off all points ofair egress to the outlet 15.

When current is applied to the terminals 21 and 22, the coil 20 isenergized and induces an axially oriented magnetic field in the magneticcircuit which is provided as follows: the magnetic field passes throughthe first pole piece 1, across the air gap 17 and through the plunger 5to the second pole piece 18, the return path for the magnetic fieldbeing from the pole piece 18 into the stainless steel housing 4 andpassing around the coil and through the wall back into the first polepiece 1. The housing is formed of magnetically permeable stainlesssteel. Thus, the entire magnetic circuit is defined by non-corrosivepermeable materials.

Upon energization, the plunger 5 is attracted by the first pole piece 1and slides with the seal 3 to suddenly open the outlet port 15 byconnecting it to the inlet port 14 through inlet passage 13 and valvechamber 16. This allows high pressure air to pass to the outlet port 15.The magnetic attraction between pole piece 1 and plunger 5 acts againstthe force of the spring 2 and, upon the removal of the magnetic field,the spring forces the plunger 5 to return into sealing engagement withthe face seal 12.

It can be seen that the plunger moves rapidly when the coil is energizedand provides communication between the valve chamber 16 and the outlet15 along a 360 degree port opening, this action taking place rapidly toprovide the type of action depicted in the curves of FIGS. 1 and 2 forthe full flow embodiment.

FIG. 2 is a plot of the flow areas for the conventional valve as opposedto the full flow solenoid valve in accordance with the presentinvention. With the conventional solenoid valve, as, for example, thatdepicted in the above noted Chelminski patent, the plunger 82 thereonslides past the holes 108 in valve stem 76, thus uncovering the holesand providing the flow area for the discharge air. As can be seen fromFIG. 2, there is a dramatic increase in the flow area for the valve ofthe present invention as opposed to that of the prior art.

It should also be noted that both conventional and the full flowsolenoid valves in accordance with the subject disclosure must bebalanced with pressure in order to operate properly. This means that thesolenoid plungers must be sealed in such a way that an additional loadis not placed on the plunger due to the pressure. This result isachieved in the prior art as depicted in the above noted Chelminskivalve by O-rings 160 and 84. Because both O-rings seal at the samediameter, there is no force due to the air pressure surrounding theplunger 76. The magnetic force need only pull against the force of thespring 86. The same is true for the solenoid valve of the presentinvention. The pressure is sealed from the plunger by O-ring 3 and faceseal 12. The plunger sealing diameter is the same for the plunger faceand O-ring 3. This balanced design is required in order to make thesolenoid valve sufficiently small for attachment to the air gun. Also,the solenoid coil would have to be much larger in order to provide theadditional plunger pull. This would also require a much largerelectrical current, thus requiring larger electrical cabling which couldmake the valve impractical. Within the size restrictions of the solenoidvalve (to fit the existing air guns), the subject solenoid valveachieves the higher air flow rate without increasing the overall valvesize.

Though the invention has been described with respect to a specificpreferred embodiment thereof, many variations and modifications willimmediately become apparent to those skilled in the art. It is thereforethe intention that the appended claims be interpreted as broadly aspossible in view of the prior art to include all such variations andmodifications.

I claim:
 1. A valve assembly for controlling the firing of an air gun,comprising:a valve housing; fluid inlet port means terminating in anannular chamber within said housing; fluid outlet port means terminatingin a circular outlet chamber coaxial with and adjacent to said annularchamber within said housing; valve port means within said housing meanscomprising an annular face seal disposed between and adjacent to bothsaid annular chamber and said circular chamber and reciprocable annularplunger means adapted through reciprocal movement to engage anddisengage said face seal to isolate and communicate said annular chamberand said circular chamber; and plunger actuation means within saidhousing adapted to selectively effect said reciprocal movement of saidplunger means.
 2. The apparatus of claim 1, wherein said plungeractuation means comprises a spring for continuously biasing said plungermeans away from said face seal and controllable propelling means formoving said plunger means toward and against said face seal incontravention to said spring.
 3. The apparatus of claim 2, wherein saidspring is coaxial with said plunger means and at least partiallycontained therein.
 4. The apparatus of claim 3, wherein said plungermeans is comprised of a magnetically permeable material and saidpropelling means comprises a solenoid coil disposed about said plungerand adapted to selectively generate a magnetic field.